CONNECTORS IN FIXED PARTIAL DENTURE.pptx

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1. CONNECTORS IN FIXED PARTIAL DENTURE GUIDED BY DR.R. VENKAT MDS,PHD (READER) DR.B. MUTHUKUMAR MDS (PROF &HOD) PRESENTER D.ARUN ROSAN II YR PG

2. CONTENTS INTRODUCTION DEFINITION DESIGN AND REQUIREMENTS OF CONNECTORS TYPES AND CHOICE SELECTION INDICATIONS OF EACH CONNECTOR ADVANTAGES AND DISADVANTAGES MATERIAL SCIENCE A. SOLDERING B. SOLDERING FLUX AND ANTIFLUX C. SOLDERING INVESTMENT D. HEAT SOURCE

3. CONTENTS SELECTION OF TECHNIQUES A. PRE-CERAMIC SOLDERING B. POST -CERAMIC SOLDERING C. OVEN SOLDERING D. TORCH SOLDERING F. INFRA RED SOLDERING PROCEDURE A. OCCLUSAL SOLDERING INDEX (PLASTER OR ZNOE) B. AUTO-POLYMERIZING INDEX C. WAX REMOVAL AND PREHEATING D. SOLDERING CONNECTOR FAILURES SUMMARY REFERENCES

4. INTRODUCTION CONNECTORS,THE TERM ITSELF INDICATES CONNECTOR

5. DEFINITION In fixed prosthodontics, the portion of a fixed partial denture that unites the retainers and pontics . GPT 9

6. DESIGN AND REQUIREMENTS OF CONNECTORS Wide enough to provide strength to the unit, not wide enough to hamper the oral hygiene maintenance. Occupy the normal interproximal areas – preserve the embrasure. Placed lingually and incisally – esthetics Gap width of 0.25 mm.

7. V-shaped grooves at the fixed joints should be avoided in the wax-up and should be replaced with regular shaped U-grooves in which the ratio of the radius of the groove to its depth (r/d) is as large as possible . Doubling the depth of the connector increases its strength. A connector of 1.5 mm depth (a) will be increased in strength by a factor of eight if the depth is increased to 3 mm (b).

8. A connector of width 1.5 mm (a) will be doubled in strength when increased to 3 mm (b). If a one-tooth pontic bridge (a) is compared with a two-teeth pontic bridge (b) and the design of the pontics and connectors remains unchanged, then the two-teeth bridge will bend eight times as much as the one-tooth bridge.

9. High tensile stresses may occur at the linguocervical area of the abutment crowns. When the metal collars are too thin flexure may occur. This area must be reinforced with metal to prevent distortion of the cervical margins. Anteriors connectors involving more than one pontic should have the lingual metal extended to the surface. For maximum aesthetics and where the metal is of adequate thickness (2.5 to 3 mm) the connectors may be extended to the surface at the joint area only.

10. Connectors should have the maximum depth occluso-gingivally without impinging on the gingival tissue . Where the occluso -gingival depth is limited, connectors should be extended onto the occlusal surface .

11. Optimum aesthetics will be obtained if the connectors are extended to the surface at the joint area only, providing the metal substructure is of adequate thickness.

12. RIGID CONNECTORS A cast, soldered, or fused union between the retainer(s) and pontic (s). CAST SOLDERED LOOP CONNECTORS NON RIGID CONNECTORS Any connector that permits limited movement between otherwise independent members of an FPD TENON- MORTISE SPLIT PONTIC CROSS PIN AND WING CONNECTOR DOVE – TAIL

13. RIGID CONNECTORS

14. INDICATION These connectors are used when the entire load on the pontic is to be transfered directly to the abutments. CONTRA INDICATIONS : D iastema to be maintained. T ilted abutments. Abutments with differing long axis. long span bridges.

15. CAST CONNECTORS shaped in wax as part of a multiunit wax pattern . DISADVANTAGES The fit of the individual retainers may be adversely affected because distortion occurs more easily when a multiunit wax pattern is removed from the die system. . ADVANTAGES Cast connectors are convenient and minimize the number of steps involved in the laboratory fabrication RESTRICT CAST CONNECTORS TO Complete coverage restorations which can be gripped buccolingually

16. SOLDER CONNECTOR Intermediate metal alloy is used whose melting temperature is lower than that of the parent metal Connectors to be soldered are waxed to final shape and sectioned with a thin ribbon saw . So that when the components are cast, the surfaces to be joined will be flat,parallel , and a controlled distance apart. This ensures accurate soldering with a minimum of distortion.  SOLDERING GAP WIDTH :- optimum Gap width ranging from 0.13 to 0.3

17. NON RIGID CONNECTORS TYPES Dove tail connectors (key and ways) or ( tenon – Mortise) Loop connectors Split pontic Cross pin and wing connectors

18. INDICATON   Malaligned abutments without common path of insertion Existence of pier abutments Long span FPD s, which can distort due to shrinkage of porcelain Distal abutment with questionable prognosis Presence of numerous mobile teeth which need to be splinted by fixed restoration CONTRAINDICATION Teeth with large pulp chambers Abutment with reduced clinical crown 

19. Dovetail slide attachment By prof.Beyler Posterior This technique is best suited for releiving stress at midspan on long pontics . Consists of a mortise (female) prepared within the contour of the retainer and a tenon (male) attached to the pontic . P eriodontically weakened abutments. long fixed partial dentures. H eavy occlusal forces. DOVETAIL

20. ADVANTAGES: 1)Relieve stress on abutments. 2)Acts as a splint of periodontically weakened teeth. 3)Allows for easy repair. In case of fracture, not the whole assembly has to be repaired only the defective segment has to be removed and repaired. DISADVANTAGES: 1)Time consuming 2)Cost factor. 3)Require extensive tooth prepration .

21. Deep wax box- distal surface Of wax pattern Mortise/Female /Keyway Pontic

22. PATTERN FABRICATION : Incorporation of prefabricated inserts Wax Patterns Custom milling Pulp size and clinical crown height can be limiting factors in the design of non rigid connectors

23. A- the mesial segment ,with the keyway,is cemented first B- the distal segment ,with the key ,is cemented immediately after A B distal aspect of the anterior retainer

24. LOOP CONNECTOR Consists of a loop on the palatal aspect of the prosthesis that connects adjacent retainer or pontics . May be cast from a circular sprue wax or shaped with platinum-gold-palladium alloy. DISADVANTAGE Plaque control

25. SPLIT PONTIC This is an attachment that is placed within the pontic . It is particularly useful in tilted abutment cases, where the conventional dovetail would necessitate the drastic preparation in the distal aspect of the pier abutment.

26. ADVANTAGES : When problem occurs ,only the affected segment can be removed and repaired or remade.no need to remove the whole assembly. Stresses that are to be applied are evenly distributed. Allows some degree of movement in function and hence protects the abutment overloading. Also act as a splint. DISADVANTAGES : More time consuming. Cost factor.

27. The wax pattern for the anterior three-unit segment is fabricated first, with the distal arm attached to the pier relations. The underside of the arm is shaped like the tissue continuity area of a pontic . A surveyor is used to position either key and key way segment pointing occlusally and the segment must align with the distal abutment preparation .

28. Invest, burnout and cast the mesial third and a half unit segment . After preliminary finishing, seat the cast segment on the working cast and place the plastic pattern down into it . Wax the distal retainers at distal occlusal two-third of the pontic pattern . The pontic can be metal-ceramic, but there should be a thin collar of metal around the periphery of ceramic section . Cement the mesial segment first followed by distal segment .

29. CROSS PIN AND WING CONNECTORS : 1)The design will be primarily used to accommodate the abutment teeth with disparate long axis . Used in case of tilted molars. INDICATIONS :

30. Fabrica tion of connector : This is the working elements of a two-piece pontic system that allows the two segments, to be rigidly fixed after the retainer have been cemented on their respective abutment preparations. The path of insertion of each tooth preparation is made to parallel the long axis of each tooth. Attach a vertical wing, cut out of a piece of wax, to the mesial surface of the distal retainer wax pattern, the wing should parallel the path of insertion of the mesial abutment preparation.

31. Invest, burnout and seat the distal retainer. Seal it on the cast, and drill 0.7 mm while through the wing with a twist drill. Plane 0.7 mm lead pencil through the hole and build the wax pattern around the lead and the wing .Place 0.7 lead pencil in the pontic during investing so that the hole will be there in the pontic . Assemble the two parts of the fixed partial denture on the working cast, use a reamer and smoothen the hole in the pontic . .

32. Fabricate a pin of the same alloy used for fixed partial denture. It must be long enough to extend all the wax throughout the pontic cone assembly. Try the pins for fit on the components on the cast. Cement the retainer with the wing first followed by the retainer pontic segment. Seat the pin in the hole with a punch and mallett . Remove any excess length both facially and lingually

33. ADVANTAGES: 1)NO NEED TO REMOVE THE WHOLE ASSEMBLY IF REQUIRED. 2)STRESS DISTRIBUTION. 3) R EDUCES THE AMT OF FORCE ON ABUTMENTS. DISADVANTAGES : 1)TIME FACTOR. 2)ADDITIONAL LABORATORY STEPS REQUIRED FOR PIN FABRICATION. 3)TECHNIQUE SENSITIVE .

34. A LOCKING ROD AND TUBE CONNECTOR Ronald A Bryant, and Robert R,Faucher , (1983) Describes two methods for interlocking the segments of fixed splints. Solderless joints where the connector occurs between adjacent abutment teeth .

35. 2) A locking rod and tube attachment when the connector occurs in a Pontic space. The locking rod and tube attachment allows complete independence of each segment. If problems occur in any segment of the splint, only that segment must be removed to make a repair. _

36. AN ALTERNATIVE ORIENTATION OF NONRIGID CONNECTORS IN FIXED PARTIAL DENTURES Moulding MB., Holland GA., & Sulik WD. (1992) Described an alternative orientation of nonrigid connectors in fixed partial dentures to overcome space limitations which may require over reduction of the preparation or over contouring of the retainer to place to keyway within the retainer wall . CONVENTIONAL ORIENTATION

37. With this alternative orientation the key is attached to the distal surface of the mesial retainer in a dual abutment fixed partial dentures, and the keyway is incorporated in the mesial surface of the pontic . This alternative orientation of nonrigid connectors in FPDs has the following advantages ( 1) conventional tooth abutment preparations with less reduction. ( 2) Suitable axial contours, ( 3) Simplified angulation and placment of the nonrigid connector with mesially inclined posterior abutment, ( 4) Improved esthetics with porcelain. (ALTERNATIVE ORIENTATION)

38. SOLDERING: IN SOLDERING METAL PARTS ARE JOINED TOGETHER BY MELTING A FILLER PARRTICLE BETWEEN THEM AT A TEMPERATURE BELOW THE SOLIDUS TEMPERATURE OF METAL BEING JOINED AND BELOW 450° BRAZING: IN BRAZING METAL PARTS ARE JOINED TOGETHER BY MELTING A FILLER METAL BETWEEN THEM AT A TEMPERATURE BELOW THE SOLIDUS TEMPERATUREOF THE METAL BEING JOINED AND ABOVE 450° WELDING: IS THE PROCESS DURING WHICH A PORTION OF THE METAL BEING JOINED IS MELTED AND FLOWED TOGETHER. SOLDERING,BRAZING AND WELDING

39. MATERIAL SCIENCE : SOLDER TYPES : . According to Hardness : Soft solders eg . Lead tin alloys with a low melting point. Hard solders eg . Dental gold solders, silver solders. . According to Technique : Free hand soldering ; used in assembling orthodontic and other assemblies. Investment soldering ; used in bridges and restoration .

40. PRECERAMIC SOLDERS : are obviously high fusing alloys, fusing only slightly beneath the softening point of the parent alloy to be jointed. POSTCERAMIC SOLDERS flows below the pyroplastic range of the procelain Ideal solder should have the following qualities : Ease of flow at relatively low temperatures. Sufficient freely flow when melted ( i.e phenomenon of wetting should be there). Strength compatible with that of the structure being soldered. Acceptable donor to give an inconspicious joint. Resistance to tarnish and corrosion. Resistance to pitting during heating and application. Low fusing than alloy.

41. SOLDERING FLUX : This substance is applied to a metal surface to remove oxides or prevent their formation. Then the solder is free to wet and spread over the clean metal surface SOLDERING ANTIFLUX : Antiflux is used to limit spreading of solder. When the metal surfaces is clean, any excess solder introduced into work gap will tend to flow into unwanted areas . Graphite . But the carbon easily evaporate at higher temperatures. A more reliable antiflux is iron oxide in chloroform

42. SOLDERING INVESTMENT : Soldering investment are similar in composition to casting investments i.e. gypsum bonded and phosphate bonded. Soldering investments should ideally contain fused quartz as their refractory component to minimize expansion (thermal ). HEAT SOURCE : It is needed to melt the filler metal. Different type of heat source used are: - 1 ) Flame 2) Oven 3 ) Infrared light. Flame It is commonly used flame is gas-air/gas –oxygen torch

43. Type of fuel used with oxygen Flame temperature Heat content Hydrogen gas 2660 275 Natural gas 2680 1000 Propane 2850 2385 Acetylene 3140 1448

44. PROCEDURE Armamentarium Autopolymerizing acrylic resin Zinc oxide- Eugenol paste Impression plaster Mixing bowl and spatula Small brush Waxing instrument Sticky wax, base plate wax, sprue wax Soldering investment Glass slab Soldering tripod Flux Solder Torch Pickling solutio n.

45. Grind the connector surfaces of the finished castings with a stone to remove the surface oxides. Then fully seat the castings on the working cast or in the mouth. The soldering gap can be adjusted at 0.25mm. Make an impression plaster registration in a small tray or on a sheet of base plate wax for the occlusal index. Index can be made with ZOE paste. Occlusal soldering index

46. Flow wax intp the connector area to prevent the investment from entry. Box the assembly with a suitable sheet wax. Mix the investment carefully and flow it into the castings without entrapping any air. Allow the invested block to bench set prior to removing the wax and preheating.

47. EFFICIENT SOLDERING INDEX MATERIALS FOR FIXED PARTIAL DENTURES AND IMPLANT SUBSTRUCTURES George CC, and Winston WL.(1995) Discussed that multiple-unit fixed partial dentures routinely require an intraoral index to ensure accurate fit. One of the most commonly used materials is Duralay acrylic resin, which has yielded satisfactory clinical results, but one disadvantage has been a prolonged setting time. This study compared the setting times of two auto polymerizing resins, Duralay and G.C.Pattern resin . The dimensional accuracy of these materials was also compared with one light-cured resin. G.C.Unifast light-cure resin . All three materials were suitable to relate castings with clinically acceptable outcomes, and chairside time could be saved with the use of recently introduced indexing materials.

48. AUTO POLYMERIZING RESIN SOLDERING INDEX An occlusal index is less suitable for the registration of anterior restorations. The thinness of the incisal edges of these units makes them less stable. STEPS : Join the completed units together with autopolymerizing resin. The resin will later burnout, leaving no residue that could interfere with the casting. Apply the resin with a bead technique because this will minimize distortion from polymerization shrinkage. The resin should extend out the incisal edges of the retainers and excessive bulk of resin reduces the accuracy of the technique . When the resin has fully hardened, carefully loosen the prosthesis from the abutments and again check for any distortion. Same way as we check the try-in of an FPD . Fill the castings with soldering investment.

49. When the resin has fully hardened, carefully loosen the prosthesis from the abutments and again check for any distortion. Same way as we check the try-in of an FPD. Fill the castings with soldering investment. The resin should extend out the incisal edges of the retainers and excessive bulk of resin reduces the accuracy of the technique. When the resin has fully hardened , carefully loosen the prosthesis from the abutments and again check for any distortion. Same way as we check the try-in of an FPD. Fill the castings with soldering investment.

50. WAX REMOVAL, AND PREHEATING : If a plaster or zinc oxide eugenol index was used, remove it after the investment has fully set. The wax can be removed using boiling water and the joint space should be free of investment. In the joint space, flow a little flux while the soldering block is still warm from the wax removal so that it will prevent small particless falling into the gap. WAX REMOVAL APPLICATION OF FLUX AND ANTILFLUX

51. Then pre heat the investment in a burnout furnace. 650°C (for low heat soldering) 850° C (for post ceramic soldering) Acrylic resin indexes are removed by heating slowly to 300° C at which time most of the resin will have burned away. Heat the block to 650°C until all traces of wax and resin have vaporized and then transfer it to the soldering stand

52. Surface preparation Clean soldering contact surfaces are a basic requirement for optimum wetting.The surfaces of thesoldering contact areashave to be prepared bygrinding and/or sand blasting . Evenly roughen the soldering contact surfaces in the direction of flow of the solder using asuitable ( ceramic-bonded)grinding instrument. The soldering contactsurfaces may also be blasted with 50 micron Al2O3 . The soldering contact surfaces should have dimensions adequate for the intended stressbearing situation .

53. Pre-Soldering (Before Ceramic Firing) Once the surfaces of the framework elements to be soldered are prepared, the individual components are placed on the model and secured.

54. Post-Soldering(After Ceramic Firing)

55. Oven soldering or Furnace Soldering : Furnace /oven soldering is dine under vacuum /air . the soldering assembly is placed in horizontal muffle with affixed floor, temperature is raised above fusion point of solder. Then muffle is opened and solder is fed unto joint space

56. TORCH SOLDERING : When torch is used to melt solder, metal ceramic restoration is preheated in the oven to avoid cracking the porcelain. Reducing zone of flame is used to prevent oxidation of joint surfaces. The flame is kept moving to prevent uncover heat distribution. During this procedure the flow of solder is controllable and used when connector has not been well designed in wax .

57. INFRA RED SOLDERING : It is used with low fusing connectors, preceramic soldered joints. specially designed apparatus & processing time. Connector area of soldering assembly must be positioned precisely relative to the focal point of the reflector that concentrates the heat, infrared energy from tungsten iodide lamp –3400 c . T he operator observes soldering procedure through protective dark screen and stops electric supply once solder flows .the joints produced have similar strength as conventional soldering .

58. Gerard .b. et all (1992) : - compared accuracy of fit of castings (F.P.Ds) with as cast connectors and infrared soldering. They found that mean marginal gap was – 65.2(for cast connectors) 18.9(infrared soldered connector) it was also observed the F.P.Ds with infrared soldered connectors showed better fit than as cast connectors and to similar to single retainer castings

59. A Three-Dimension Finite Element Analysis to Evaluate the Stress Distribution in Tooth Supported 5-Unit Intermediate Abutment Prosthesis with Rigid and Nonrigid Connector Oblique forces produce more stresses than vertical forces. Nonrigid connector resulted in decrease in stress at the level of prosthesis and increase in stress at the level of alveolar crest . Modi , Ritesh et al. “A Three-Dimension Finite Element Analysis to Evaluate the Stress Distribution in Tooth Supported 5-Unit Intermediate Abutment Prosthesis with Rigid and Nonrigid Connector.”  European Journal of Dentistry  9.2 (2015): 255–261 ..

60. Kamposiora p et al (1996) 11 studied the stress concentration of all ceramic posterior fpd’s maximum stress found was Material Diameter of connector Maximum stress Gold 3MM 20.5   4MM 12.5 DICOR 3MM 19.4   4MM 12.5 INCERAM 3MM 12.5   4MM 7.5       Higher stress was found in the apical region of connector & least in middle part of connector. So they advised to increase the height of connector to increase the bulk and have good stress distribution, and have smooth geometry as compared to angulated geometry in short connectors. It was recommended to use 4*4mm connector size for ceramic 2*3mm for metal Kamposiore et al “Stress concentration in all-ceramic posterior F.P.D”Qint . int 27(10),701-706

61. Connectors for provisional restorations The connectors for provisional restorations should be carefully fabricated due to the low strength of the material usually used. They should be slightly overcontoured for increasing strengthening. Decrease the sharpness at the junction this relieves the stress concentration which may lead to fatigue failure of restoration. Use high strength materials such cast metals, heat-processed resin fiber reinforced.

62. Connectors for all ceramic fpd’s Kamposiora p et al (1996) 11 studied the stress concentration of all ceramic posterior fpd’s maximum stress found was Material Diameter of connector Maximum stress Gold 3mm 20.5 4mm 12.7 Dicor 3mm 19.4 4mm 12.5 Inceram 3mm 12.5 4mm 7.0

63. Connectors for all ceramic fpd’s It was found that stress concentration was found more in region of force applied and at connector region. And stress levels were higher in 3.0mm than in 4.00 mm at connector. Higher stress was found in the apical region of connector & least in middle part of connector. So they advised to increase the height of connector to increase the bulk and have good stress distribution, and have smooth geometry as compared to angulated geometry in short connectors. It was recommended to use 4*4mm connector size for ceramic 2*3mm for metal.

64. Connectors for metal ceramic Berger Robert (1989) 16 described the esthetic and physiologic consideration in metal framework design The amount of beam distortion is L2 * D3 There should be no beam distortion to prevent porcelain fracture. So for long span fpd’s connectors size should be increased. The interproximal zone should have adequate span for porcelain and connector placed lingually .

65. Connectors for cantilever bridges Hong so yand et al (1996) 13 : - stress analysis of a cantilevered fps with normal and reduced bone support. Studied the mechanical behavior of a cantilever fpd with normal and reduced bone support. They found high stress concentrations were found around the connector of fpd .

66. Design of fpd should be such that occlusal forces are limited to the connector’s ability to accept them. Greatest stress was seen in distal cantilevered prosthesis and stress was seen distal to the most distal retainer and fracture may occur at this location. Cantilevered fpds should limit to replacement single tooth only and also use splinting of abutments.

67. Connectors for tooth implant supported fpd’s Mahamoud h et al (2000) 7 performed a 14 yr comparison of connected and non-connected tooth-implant fpd’s . The difference in mobility of tooth (50-200  m) and implant (10  m). This difference can lead to intrusion of abutment, fracture of abutment teeth, fracture of implant component, increased marginal bone loss and loss of Osseo integration. Rangert et al (1997) stated that implant connected to tooth will act as cantilever. Cohen s r et al (1994) advocate use of non-rigid connection between teeth and implants. To limit cantilever forces and direct occlusal loads axially to the implant.

68. CONNECTOR FAILURES A connector between an abutment retainer and a pontic or between two pontics can fracture under occlusal forces, failures of both cast and soldered connections have been observed and are generally caused by internal porosity that has weakened the metal.

69. When fracture occurs, pontics are placed in a cantilevered relationship with the retainer casting, and this can allow excessive forces to be developed on the abutment tooth. For this reason, the prosthesis should be removed and remade as soon as possible. Modified sanitary pontic design gives optimum connector design with least gingival irritation.

70. The main causes of connector failure:- Improper design Weak framework Incomplete flow /crystallization of the soldered joints. Porosities can result in either soldered/ cast connectors that may lead to failures .

71. If abutment castings can be removed, they can be indexed, resoldered and recemented . If removal is unsuccessful it may be necessary to be remade some/ all of the units of the restoration. In special situations / where extensive restorations are involved an innovative techniques may be used with good results.

72. S ummary The prognosis of an fixed partial denture will depend on occlusion, span length, bone loss and quality of periodontium . Since majority of stress are concentrated at the connector area of the fixed partial denture, they have to be precisely made . Connector should be large enough so that it can resist the forces and at a same time it should be aesthetically pleasing and should be in harmony with embrassure space

73. A soldering index made with 4-meta adhesive resin. J. Prosthet Dent 1994; 72 : 430-2. Fatigue life of preceramic sodlered and postceramic soldered joints. Int J Prosthodont 1993; 6 : 468-474. Torch versus oven preceramic soldering of a nickel chromium alloy. Quintessence Int 1993; 21 : 753-757. An alternative orientation of nonrigid connectors in fixed partial dentures. J. Prosthet Dent 1992; 68 : 236-8. Post ceramic soldering of various alloys. J Prosthet Dent 1982; 48 : 686-689. Efficient soldering index materials for fixed partial dentures and implant substructures. J Prosthet Dent 1995; 73: 424-7. A locking rod and tube connector. J. Prosthet Dent 1993; 49 : 647-651. REFERENCES

74. The seating of one piece and soldered fixed partial dentures. J Prosthet Dent 1989; 62: 292-7. Use of the split pontic nonrigid connector with the titlted molar abutment. J. Prosthet Dent 1986; 36: 249-251. The fit of fixed partial dentures joined by infrared soldering. J Prosthet Dent 1992; 68: 591-6. Cast connectors : An alternative to soldering base metal alloys. J. Prosthet Dent 1986; 55: 195-197. Accuracy of one piece castings, preceramic and postceramic soldering. J. Prosthet Dent. 1986; 55: 312-317. The effects of prewetting on postsoldering of base metal alloys. J. Prosthet Dent. 1985; 54: 355-358. Soldering porcelain fused to metal fixed partial dentures. J. Prosthet Dent. 1973; 30: 918-921. Comparison of accuracy of soldering indices for fixed prostheses. J. Prosthet . Dent. 1978; 40: 35-38. Contemporary Fixed Prosthodontics . Rosensitel 4 st Edition